Fuel cell systems employing evaporative cooling, such as in U.S. Pat. No. 7,504,170 (incorporated herein by reference) require condensing heat exchangers that are compact and efficient. This is especially so in fuel cell systems used in mobile applications, such as electric vehicles powered by fuel cells. Plate-fin type heat exchangers and finned tube type heat exchangers are suitable for such use. These heat exchangers, however, generally consist of very narrow flow channels with very dense heat transfer fins and tubes or plates to maximize the heat transfer area in the condensation flow side, within the limited space.
Because the condensation channels are so narrow, when a fuel cell system is shut down, water easily remains in the flow channels due to the lack of a sufficient moving fluid volume to conduct the condensate. The condensate tends to pool across the narrow channels after shutdown and will freeze in sub-freezing environments. The next startup is hampered since the air flow channels are partly or entirely blocked by ice. Furthermore, ice blockage will create structural stresses which may damage the condenser. In some situations, particularly if both the condensate flow and the cooling flow are required to be horizontal, condensate water may pool up and plug some of the flow channels during operation of the fuel cell system, especially during low-power operation.